I have always thought the 'taking of the test' needed more security, and that parents will take drastic measures to get the 'pass' even if they are not going in for the test themselves!! The need for a letter, pupil name and date of birth is not sufficient. The parents often have a choice regarding the venue of the test and could easily put another child in for the exam as their own if they wished, at a place which is so busy no-one would catch-on that there was an imposter. I would bet that some children sitting these entrance exams are not the named pupils on the school's list!!! Or am I just nuts????!!!!!
I seem to remember the book was quite harmless (that was 3 years ago though so forgive me if I'm wrong!!) but Tv productions often seem to add some interesting "extras" that did not appear in a book. Could be one of those you have tp watch the DC get to see it (or not!!)